Example
CASE's shorthand variant evaluates an expression (usually a column) against a series of values. This variant is a bit shorter, and saves repeating the evaluated expression over and over again. The ELSE clause can still be used, though:
SELECT Id, ItemId, Price,
CASE Price WHEN 5 THEN 'CHEAP'
WHEN 15 THEN 'AFFORDABLE'
ELSE 'EXPENSIVE'
END as PriceRating
FROM ItemSales
A word of caution. It's important to realize that when using the short variant the entire statement is evaluated at each WHEN. Therefore the following statement:
SELECT
CASE ABS(CHECKSUM(NEWID())) % 4
WHEN 0 THEN 'Dr'
WHEN 1 THEN 'Master'
WHEN 2 THEN 'Mr'
WHEN 3 THEN 'Mrs'
END
may produce a NULL result. That is because at each WHEN NEWID() is being called again with a new result. Equivalent to:
SELECT
CASE
WHEN ABS(CHECKSUM(NEWID())) % 4 = 0 THEN 'Dr'
WHEN ABS(CHECKSUM(NEWID())) % 4 = 1 THEN 'Master'
WHEN ABS(CHECKSUM(NEWID())) % 4 = 2 THEN 'Mr'
WHEN ABS(CHECKSUM(NEWID())) % 4 = 3 THEN 'Mrs'
END
Therefore it can miss all the WHEN cases and result as NULL.
